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Life Science Notes Chapter 3 3.1 Chemistry of Life Matter is anything that has mass and takes up space. Energy- is anything that brings about change. Energy can hold matter together or break it apart. Atom are small particles that makes up matter. At the center of an atom is a nucleus that contains protons and neutrons Protons have a positive charge, and neutrons have no charge. Outside of the nucleus are electrons which have a negative charge. Electrons are the part of the atom that are involved in chemical reactions. An atom is mostly empty space. Energy holds the parts of an atom together. When something is made up of only one kind of atom it is called an element An element can’t be broken down to a simpler form by chemical reactions. Scientists have given each element a one or two letter symbol All elements are arranged in a chart known as the periodic table of elements. Compounds are made up of two or more elements in exact proportion. There are two types of compoundsmolecular and ionic. The smallest part of a molecular compound is a molecule. A molecule is a group of atoms held together by the energy of chemical bonds. When chemical reactions occur, chemical bonds break, atoms are rearranged, and new molecules form. 6CO + 6H O + energy = C H O6 + 6O 2 6 12 2 2 Molecular compounds form when different atoms share their outer most electrons. Atoms also combine because they’ve become positively or negatively charged. Atoms are usually neutral- they have no overall electric charge. When an atom loses an electron it becomes positively charged. When an atom gains an electron it becomes negatively charged. Electrically charged atoms are called ions Ions of opposite charges attract one another to form electrically neutral compounds called ionic compounds. Table salt is made of sodium and chlorine ions. Potassium and sodium ions help nerve cells send messages. Calcium ions make muscles contract. A mixture is a combination of substances in which individual substances retain their own properties. Mixtures can be solids, liquids, gases or any combination of them. Most reactions in living organisms take place in mixtures called solutions. In a solution 2 or more substances are mixed evenly. A suspension is formed when a liquid or a gas has another substance evenly spread throughout it. Unlike solutions, the substances in a suspension eventually sink to the bottom. Rocks and other nonliving things contain inorganic compounds. Organic compounds always contain carbon and hydrogen and usually are associated with living things. Four groups of organic molecules make up all living things- Carbohydrates, lipids, proteins and nucleic acids. Carbohydrates are organic molecules that supply energy for cell processes. Sugar and starches are carbohydrates that cells use for energy. Some carbs are also important parts of cell structures like parts of the cell membrane. Lipids do not mix with water. Lipids such as fats and oils store and release even larger amounts of energy than carbohydrates do. Proteins are made up of smaller molecules called amino acids. Proteins are the building blocks of many structures in organisms. Certain proteins called enzymes regulate all chemical reactions in cells. Large organic molecules that store important coded information in cells are called nucleic acids. One nucleic acid, deoxyribonucleic acid, or DNA-genetic material- is found in all cells at some point in their lives. Another nucleic acid, ribonucleic acid or RNA is needed to make enzymes and other proteins. Most inorganic compounds are made from elements other than carbon. Inorganic compounds are the source for many elements needed by living things. Inorganic compounds can contain the elements nitrogen, phosphorus, and sulfur. One of the most important inorganic compounds for living things is water. Living things are made of more than 50% water and depend on water to survive. Seeds and spores of plants, fungi and bacteria need water if they are to grow and reproduce. All chemical reactions take place in water solutions, and organisms use water to move materials through their bodies. The atoms of a water molecule are arranged in a way that the molecule has areas with different charges. Water molecules are like magnet. This attraction between water molecules makes the surface like a film. This is the reason that bugs can walk on it. Because water molecules are so strongly attracted to each other, the temperature of water changes slowly. The large % of water in living things acts like an insulator. The water in a cell helps keep its temperature constant, which allows life sustaining chemical reactions to take place. When water freezes ice crystals form. In the crystals, each water molecule is spaced at a certain distance from all others. Because this space is greater in frozen water than in liquid water, ice floats on water. Bodies of water freeze from the top down. The floating ice provides insulation and allows living things to survive. 3 .1 Moving cellular Materials Cells take in food, oxygen and other substances from their environment. They also release waste materials. A cell has a membrane around it that works like a window screen. A cells membrane is selectively permeable It allows some things to enter and leave the cell while keeping other things outside or inside the cell. The movement of substances through the cell membrane without the input of energy is called passive transport. There are 3 kinds of passive transport. The movement of molecules from areas where there are many molecules to areas where there are few molecules is called diffusion. Molecules will continue to move until the areas are equal. When this occurs equilibrium is reached and diffusion stops. Water molecules move by diffusion into and out of cells. The diffusion of water through the cell membrane is called osmosis. Some substances are too large to pass with diffusion so they can only enter with the help of molecules. Usually these molecules are transport proteins. This process still doesn’t require energy and it is called facilitated diffusion. When input of energy is required to move materials through the cell membrane, active transport takes place. The process of taking substances into a cell by surrounding it with the cell membrane is called endocytosis. Some one-celled organisms take in food this way. Exocytosis occurs in the opposite way as endocytosis. A vesicles membrane fuses with the cell membrane and the vesicles contents are released. .1 Energy For Life The total of all chemical reactions in an organism is called metabolism. The chemical reactions of metabolism need enzymes. Enzymes in cells cause change but the enzyme does not change. It can be used again. They can cause molecules to join or break apart. Without the right enzyme a chemical reaction cannot take place. Each chemical reaction in a cell requires a specific enzyme. Organisms that make their own food, such as plants are called producers. Organisms that cannot make their own food are called consumers. During photosynthesis producers use light energy to make sugars, which can be used as food. The captured light energy is used to drive the chemical reactions during which the raw materials carbon dioxide and water are used to produce sugar and oxygen. For plants, raw materials come from air and soil. Some of the captured light energy is stored in the chemical bonds that hold sugar molecules together. Plants make more sugar during photosynthesis than they need for survival. Excess sugar is changed and stored as starches or used to make other carbohydrates. Plants use carbohydrates as food for growth, maintenance and reproduction. Consumers take in food by eating producers or other consumers. Some of the energy from the food you eat is used to make you move. Some of it becomes thermal energy, which keeps you warm. Most cells need oxygen to break down food. During cellular respiration chemical reactions occur that break down food into simpler substances and release their stored energy. Enzymes are needed just like in photosynthesis. The type of food most easily broken down by cells is carbohydrates. Respiration of carbohydrates begins in the cytoplasm of the cell. The carbohydrates are usually broken down into simpler molecules. Glucose is broken down into two simpler molecules. As glucose molecules are broken down, energy is released. The two simpler molecules are broken down again. This breakdown occurs in the mitochondria of the cells of plants, animals, fungi and many other organisms. This process uses oxygen releases much more energy and produces carbon dioxide and water as wastes. When you exhale you breathe out carbon dioxide and some of the water. Respiration occurs in the cells of many living things. When cells do not have enough oxygen for respiration they use a process called fermentation to release some of the energy stored in glucose molecules. Like respiration, fermentation begins in the cytoplasm. Again as the glucose molecules are broken down, energy is released. But the simple molecules from the breakdown of glucose do not move into the mitochondria. Instead, more chemical reactions occur in the cytoplasm. The reactions produce some energy and produce wastes. Depending on the type of cell, the wastes may be lactic acid alcohol and carbon dioxide. The presence of lactic acid is why your muscles might feel stiff and sore after you exercise. During photosynthesis and respiration, what is produced in one is used in the other. Photosynthesis produces sugars and oxygen, and respiration uses these products. The carbon dioxide and water produced during respiration are used during photosynthesis.